1. Field of the Invention
The present invention relates to a touch switch structurally characterized in that a plurality of operation units are provided adjacent to each other and a vehicle interior lighting device equipped with the touch switch, more particularly to a touch switch having an excellent operability and capable of appropriate detecting contacts made by a human body part with the operation units irrespective of sizes, structures, and layout of the operation units, and a vehicle interior lighting device equipped with the touch switch.
2. Description of the Related Art
Conventionally, as a switch for a vehicle interior lighting device, such as a room lamp for vehicle provided in an indoor ceiling of an automobile, a touch switch which detects a capacitance variation caused by contact made by a human body part for a switching operation is considered. The touch switch is structurally characterized in that operation faces can be provided integral with light sources, and illumination can be turned on/off by directly touching a portion of the light sources per se. Therefore, a vehicle interior lighting device where the touch switch is used is compact in size and superior in operability.
In many of the vehicle interior lighting devices, a plurality of light sources, such as a dome lamp which illuminates the whole vehicle interior and spot lamps which respectively illuminate different seats of the vehicle, are arranged side by side in a part of the vehicle ceiling. Therefore, plural operation faces for manipulating the light sources need to be arranged side by side likewise, and detectors of the operation faces provided to detect contacts by a human body part are disposed next to each other. In these vehicle interior lighting devices, unintended operations often start whenever a boundary between the panels or anywhere nearby is accidentally contacted by a human body part. In the case where such an event occurs, it is difficult to decide accurately which one of the operation faces was actually contacted, and therefore, it becomes necessary to avoid any irregular switching operation by preventing the two adjacent operation faces from concurrently responding to the contact.
To deal with the conventional problems, a vehicle interior lighting device was disclosed, wherein an area dimension of a part of the detector currently contacted by a human body part is detected, and light sources to be turned on/off are changed depending on the detected contact area (see the Related Art 1).
Related Art 1 JP-A-2011-46211
In the vehicle interior lighting device disclosed in the Related Art 1, two map lamps and one dome lamp are all provided in a section thereof, and six operation faces are provided as examples of the touch switch for controlling these light sources. An area dimension of an object in proximity of or in contact with any of the operation faces is measured based on a capacitance magnitude, and which of the light sources should be turned on/off is decided through comparison for each of the operation faces.
When a fingertip trying to carry out an operation is near a boundary between two operation faces, however, capacitance variations in the two operation faces are almost equal, making it difficult to decide which of the switches was actually touched.
Another problem is structural restrictions in some of the vehicle interior lighting devices; some regions of these devices may not be available for detection electrodes provided to detect contact made by a human body part, for example, where components are mounted and through holes for light transmission from the light sources are formed, and the capacitance magnitude cannot be accurately detected in the case where these regions are contacted by a human body part. Therefore, a device adapted to detect a contact-based capacitance variation in such regions as well as any other regions is a long-awaited technical solution.